1. Field
The present invention is related to an air compressor suitable for producing compressed air which is required in order to drive, for instance, a pneumatic tool. More specifically, the present invention is directed to such an air compressor capable of cooling heat generating units such as a circuit board, a motor, a compressor, and the like in a higher efficiency, while the circuit board contains inverter control means.
The present invention is also related to an air compressor equipped with a main body cover and an operation panel.
2. Description of the Related Art
For instance, in construction sites, pneumatic tools for driving nails and screws into timber by utilizing pressure of compressed air are widely utilized. In general, air compressors for driving pneumatic tools have been constructed as follows: That is, rotary motion of rotation power shafts of driving units of motors and the like is converted into reciprocating motion of pistons provided within cylinders via crank shafts of compressed air generating units, and then, air sucked from air intake valves of the cylinders is compressed by the reciprocating motion of the pistons. The air compressed within the cylinders is emitted from exhaust valves of the cylinders via pipes to air tanks, and then, the compressed air is stored in the air tanks.
In such a case that an air compressor is arranged by two sets of air tanks, the air compressor contains two pieces of substantially cylindrical-shaped air tanks, and a frame which couples these two air tanks to each other by being separated from each other by a constant distance, while these two air tanks are installed in a parallel manner. Both a driving unit and a compressing unit (compressed air generating unit) are set on the upper side of the frame. Air compressed by the compressing unit is emitted to one of the two air tanks. While these two air tanks are communicated with each other via a pipe, since the compressed air is supplied from one air tank via the pipe to the other air tank, pressure within one air tank is kept equal to pressure within the other air tank. While pneumatic tools such as nailing machines are employed in order to utilize the compressed air which is stored in this air tank, high pressure of the compressed air is adjusted to proper pressure by a pressure reducing valve mounted on the air tank, and then, the pressure-controlled compressed air is supplied via an air hose to the pneumatic tools and the like. This sort of air compressors are disclosed in, for instance, JP-A-2006-188954.
The air compressor of JP-A-2006-188954 is equipped with an air tank, a motor unit, and a main body cover which covers a compressing unit. Then, electric power is supplied to a motor for driving the compressing unit by detecting a rotation position of a rotor of the motor, and also, by controlling both a current and a voltage, which are applied to a stator coil of the motor, in response to the detection signal of the rotation position. Very recently, in air compressors, inverter control means are widely used in order to drive motors in higher efficiencies, so that power consumption can be reduced.
Circuits for controlling inverters are arranged by employing semiconductor switching elements and other electronic components. While the semiconductor switching elements are under operation, heat generations from the semiconductor switching elements are large, so that these semiconductor switching elements are required to be cooled. If the semiconductor switching elements are operated under insufficient cooling conditions, then these switching elements are destroyed due to heat generations, so that control operations for motors can be no longer carried out by the inverter control circuits. As a consequence, in general, the following protection means is conducted. That is, while protection circuits are provided in control circuit unit 5, when temperatures of these electronic components are reached to predetermined temperatures, the protection circuits interrupt the supply of electric power to the motors so as to prevent destruction of the semiconductor switching elements. If the supply of the electric power is interrupted, then there is such a demerit that compressing operations of the air compressors are stopped every time the supply of the electric power is interrupted.
Very recently, while such pneumatic tools as not only nailing machines, but also screw drivers are widely utilized which are driven by using compressed air, operation frequencies of air compressors are increased in connection with increasing of consumption amounts of the compressed air. As a consequence, in air compressors with employment of inverter control means, the below-mentioned aspects are expected. That is, it is desirable to prevent overheat phenomena of inverter control circuits, and also desirable to reduce frequencies at which the operations of the air compressors are stopped, since protection circuits are operated.
In a conventional technique, an inverter control circuit unit equipped with heat generating components is stored in a storage case made of an aluminum material, or the like, which has a better thermal conducting characteristic, in such a manner that the heat generating components are closely fitted to the case. Then, the inverter control circuit unit is arranged between one pair of air tanks and below at least any one of a motor and a compressor; a portion of air flows generated by a cooling fan mounted on a compressor-sided end portion of a rotation shaft of the motor is blown to a wind duct so as to cool the heat generating components; and the wind duct is surrounded so as to be constructed by the air tanks, the compressor, the motor, and the control circuit unit.
However, when the conventional air compressor is operated in either a continuous manner or an interruption manner, temperatures at the motor unit, the compressing unit, and the air tank unit are increased due to heat generations caused by apparently the control circuit and copper losses of the stator coil of the motor, heat generations caused by friction losses of ball bearings, piston rings, and the like of the compressing unit, and further, compressing friction heat generated when air is compressed. As a result, the interior portion of the cooling-purpose air duct is brought into a high temperature condition; even when outside air is taken into the cooling-purpose air duct, the temperature at the cooling air itself is increased; and thus, the circuit elements of the control apparatus are cooled by utilizing such an air brought into the high temperature condition; so that the cooling effect is considerably lowered. If the air compressor is driven under such a poor cooling condition, then the temperature at the control circuit elements are eventually reached to a predetermined high temperature. Accordingly, there are some possibilities that the protection unit is operated, so that the operation of the air compressor is stopped.
Also, in addition to such a covering condition that the heat generating components are covered by the storage case, since the control circuit is arranged between one pair of the air tanks and located below at least any one of the motor and the compressor, as to the cooling fan mounted on the side of the compressor, such an axial flow type cooling fan must be necessarily set which is larger than the outer dimensions of the compressing unit and of the motor in order that the temperature increase occurred inside the main body cover is suppressed, and further, a sufficiently large amount of the cooling wind is blown through the wind duct formed between one pair of the air tanks. Since there is lack of the air exhausting ports for exhausting the heat stored in the interior portion of the main body cover, the temperature within the main cover is increased. As a consequence, such a large-sized axial flow type cooling fan may give a harmful influence when the main body of the compressor is designed to become compact.
Moreover, in order to avoid the above-described harmful influence, if a large-sized cooling fan is employed so as to below cooling wind through the entire interior portion of the main body cover, then the air streams are disturbed by concave and convex portions such as the compressor and the motor unit. As a result, the cooling wind cannot be exhausted in a higher efficiency outside the air compressor, which may cause a factor for increasing the temperature at the interior portion of the main body cover.
Additionally, for instance, in construction sites, pneumatic tools for driving nails and screws into timber by utilizing pressure of compressed air are utilized. Normally, compressed air which constitutes power of pneumatic tools is supplied from air compressors via air hoses to the pneumatic tools, and then, the pneumatic tools convert the supplied compressed air to power so as to drive nails and screws.
As disclosed in, for instance, JP-A-2004-300996, this sort of air compressor is constituted by an electric motor, a compressing unit, an air tank, a driving control apparatus, a fan, and a main body cover for covering these structural elements. The compressing unit is driven by the electric motor so as to suck outside air and compress the sucked outside air. The air tank stores thereinto the compressed air produced from the compressing unit. The driving control apparatus drives the electric motor. The fan cools the electric motor and the compressing unit, which generate heat by being operated.
Generally speaking, while this sort of air compressor is equipped with a pressures sensor within the air tank, the air compressor controls driving conditions thereof based upon an output signal (detected pressure) of the pressure sensor. For example, the driving control apparatus of the air compressor performs the below-mentioned control operations in order to maintain a proper amount of compressed air: That is, if compressed air stored in the air tank is decreased since the compressed air is consumed by works and thereafter detected pressure becomes lower than, or equal to a predetermined reference value (re-initiating pressure), then the electric motor is re-initiated so as to re-fill compressed air. When pressure within the air tank is returned to such a pressure value higher than, or equal to another reference value (stopping pressure), the driving control apparatus stops the electric motor.
Also, in addition to the above-explained control operation of the driving conditions of the air compressor, rotation numbers of the electric motor are changed in response to detection values of the pressure sensor so as to reduce noise; and since pressure changes occurred in the air tank are monitored, work conditions of the pneumatic tools are predicted so as to automatically change a setting value of the re-initiating pressure and the rotation number of the electric motor.
Moreover, while a power supply voltage, a power supply current, a rotation number under normal operation condition, and/or a condition as to pressure variations within the air tank are previously stored in the driving control unit, the driving control apparatus judges an abnormal condition, and notifies an occurrence of the abnormal condition from an operation panel.
As previously described, the operation panel may play an important role as a user interface. As indicated in FIG. 14, an operation panel 99 is directly fixed on an upper plane of a main body cover 8 in order to improve operable characteristics and visual recognizable characteristics. The main body cover 8 is provided in order to avoid that operators directly touch both a compressing unit 3 and an motor unit 2, which generate heat, and also, in order to form air ducts of cooling winds which are produced from cooling fans 11 and 12. As a consequence, resin materials are utilized which have superior forming characteristics and which can hardly transfer heat.
Since the main body cover 8 of the conventional air compressor 1 exemplified in FIG. 14 is formed by the resin material, the main body cover 8 has a low rigidness. Moreover, since fixed portions with respect to the rigid body are small, the main body cover 8 may be easily vibrated. As a consequence, the main body cover 8 may also be also vibrated and therefor may produce noises, since vibrations are generated when the compressing unit 1 is operated. As a result, the vibrations of the main body cover 8 may constitute one of factors which deteriorate operation environments. Moreover, there are some possibilities that large vibrations may be produced at a portion located in the vicinity of the uppermost portion of the main body cover 8, in which the operation panel 99 is arranged. Due to the above-described vibrations, there are some possibilities that disconnections may occur in a connection portion between a switch of the operation panel 99 and a power supply cable 901 connected to a power supply cord 50, and another connection portion between the switch and a signal cable 902 due to aging effects, while the operation panel 99 is mounted on the main body cover 8 in an integral body. The signal cable 902 is employed in order to transfer signals between the own signal cable 902 and a control circuit unit 5.
In addition, in such a case that the conventional air compressor 1 is assembled in production stages, or is overhauled, when the main body cover 8 is mounted on the main body of the conventional air compressor 1, since the power supply cable 901 and the signal cable 902 are tensed which are elongated from the operation panel 99, there is such a risk that contact failures of connector portions may occur. In order to prevent the occurrence of such contact failures, cable lengths of the power supply cable 901 and the signal cable 902 must be sufficiently prolonged, so that cables having extra lengths are necessarily required. In addition, in such a case that operation failures are confirmed when operations of the conventional air compressor 1 are finally confirmed after the main body cover 8 is mounted, this mounted main body cover 8 must be dismounted. Increasing of such material cost and also increasing of managing steps may constitute a factor for increasing the manufacturing cost of the conventional air compressor 1.